During a lengthy oral argument, judges were skeptical that Trump had the power to use an emergency law to enact the tariffs.

The U.S. Constitution gives the power to impose taxes — including tariffs — to Congress. But lawmakers have gradually relinquished power over trade policy to the White House. And Trump has made the most of the power vacuum, raising the average U.S. tariff to more than 18%, highest since 1934, according to the Budget Lab at Yale University.

The arguments underscored the financial stakes for U.S. importers as the Trump administration prepares to impose higher rates without the explicit approval of Congress.